Centrifugal pump assemblies are known, which comprise an axially displaceable shaft, by which means the impeller can be brought into two axial positions, wherein in a first position the flow path through the impeller is closed and in a second position the flow path through the impeller is opened. Such an arrangement is known for example from DE 101 15 989 A1. In the first position, in which the flow path through the impeller is closed, the impeller is held by a spring force, whilst given a drive motor subjected to current, it is pulled against the spring force by a magnetic force which then results, into the second position. I.e., in order to open the impeller and the pump, it is necessary for the drive motor to have a particular design which produces a magnetic axial force for moving the impeller when subjected to current.